WO2000078682A1 - Method of decomposing organic compounds in water - Google Patents

Abstract

The invention relates to a method of decomposing organic compounds in water which has a TOC content of more than 2 ppm and a content of carbonic acid and carbonates dissolved therein, by treating the mixture with ozone. The invention further relates to a method of producing chlorine by subjecting sodium chloride to an electrolysis. The inventive method is characterized in that the sodium chloride is used in said electrolysis in the form of an aqueous solution that is obtained by treating water with ozone, said water having a TOC content of more than 2 ppm and a sodium chloride content of 2 to 20 wt.- % and additional carbonic acid and carbonates dissolved therein.

Description

Process for the decomposition of organic compounds in water

The present invention relates to a process for the degradation of organic compounds in water, which has a TOC of more than 2 ppm and also contains dissolved carbonic acid or carbonates, by treatment with ozone and a

Process for the production of chlorine by electrolysis of table salt, characterized in that the table salt is fed to the electrolysis process in the form of an aqueous solution which is obtained by treating water which has a TOC of more than 2 ppm and a table salt content of 2 to 20% by weight .-% and also contains dissolved carbonic acid or carbonates, with ozone.

Methods of breaking down organic compounds in water by treating the water with ozone are known.

WO 9708101 describes the treatment of industrial waste water with ozone in

Presence of a catalyst. EP-A 634465 describes the purification of industrial waste water with ozone in a two-stage process, in particular aromatic compounds being broken down. EP-A 378994 describes the breakdown of aromatic impurities in industrial wastewater by ozone at elevated pressure and temperature.

Such as BE Gilbert in Water Res., Volume 21 (10), pages 1273-1278 describes, the use of ozone in industrially polluted wastewater generally serves to convert impurities from compounds that are not or only poorly biodegradable into components that are biodegradable. This means that even after treatment with ozone, organic compounds are present in the water, which are then used in further steps, e.g. B. a biological wastewater treatment to inorganic compounds such. B. carbon dioxide and water must be broken down. This is confirmed by Takahashi in Ozone Science and Engineering, Vol. 12, 1990, pages 1 to 18. Takahashi describes that the treatment of water containing phenol with ozone leads to the degradation of the phenol. However, that organic degradation products such. B. oxalic acid, glyoxal and glyoxalic acid arise which are not further degraded by ozone.

If water contains organic compounds, this means a certain carbon content, which is in the form of organic compounds. The carbon content, which is in the form of organic compounds, is referred to as TOC (abbreviation of "Total Organic Carbon").

Water which has a TOC of more than 2 ppm and also contains dissolved carbonic acid or carbonates is e.g. known from polycarbonate production.

To produce polycarbonates according to the so-called phase interface process, dihydroxydiarylalkanes are used in the form of their alkali salts dissolved in water with phosgene in the heterogeneous phase in the presence of inorganic bases such as e.g. Sodium hydroxide solution and an organic solvent in which the product polycarbonate is readily soluble. During the reaction, the aqueous phase is distributed in the organic phase. After the synthesis of the polycarbonate after the

Ausserdem ist das Abwasser mit organischen Verbindungen belastet wie z. B. mit Phenolen (z.B. unsubstituiertes Phenol oder Alkylphenole oder Arylphenole oderThe interfacial process separates the polycarbonate in the form of its solution in the organic solvent used in the synthesis, for example methylene chloride. The remaining aqueous phase is advantageously from volatile organic impurities such. B. Remains of the organic solvent used in the synthesis, for example methylene chloride, freed what z. B. can be done by distillation. Waste water then remains with a high content of dissolved carbonates (for example 0.3 to 1.5% by weight) and with a high content of dissolved common salt (for example 4 to 12

In addition, the wastewater is contaminated with organic compounds such. B. with phenols (eg unsubstituted phenol or alkylphenols or arylphenols or

Bisphenols such as B. bisphenol A) or amines (e.g. triethylamine or ethyl piperidine). The carbonates arise z. B. by the hydrolysis of the phosgene as a side reaction of polycarbonate production.

The sodium chloride dissolved in the wastewater of polycarbonate production using the phase boundary process is a valuable raw material. One possibility for

Utilization of the common salt in the wastewater of polycarbonate production by the phase interface process has not been described so far.

A conceivable utilization of the sodium chloride load in the wastewater of the polycarbonate production according to the phase boundary process is the use of the sodium chloride for the production of chlorine and sodium hydroxide solution by electrolysis. However, this possibility has so far failed due to the other components, in particular the organic components of the waste water from polycarbonate production using the phase interface process. In particular, the particularly advantageous membrane process of chlor-alkali electrolysis requires pure aqueous sodium chloride solutions as the starting material.

If the saline is fed to the electrolysis process in the form of an aqueous solution, this aqueous solution must contain a low content of organic impurities, preferably the TOC of the saline solution must be less than 1 ppm. Even if the TOC of the saline solution is less than 1 ppm, organic impurities may still be present to a small extent in the saline solution, which impair the electrolysis process, e.g. B. by the service life of essential system components, such as of the membranes in the case of the membrane process. All this applies in particular to the membrane process for sodium chloride electrolysis, in which the service life of the membranes is an essential factor that determines the economy.

Of course, wastewater other than that from polycarbonate production is also known, which is characterized in that it contains dissolved carbonates or carbonic acid. It is now known that carbonates or carbonic acid dissolved in water hinder the removal of organic compounds from the water by treatment with ozone, because carbonate acts as a radical scavenger and thus hinders the breakdown of organic compounds via radical intermediates, as reported by Hoigne and Bader in Wat Res , Volume 10, 1976, pages 377 ff and Gurol and Watistas m Wat Res, Volume 21, 1987, pages 895 to 900

For water that contains organic compounds and also dissolved caibonates or carbonic acid, the situation arises that treatment with ozone in the alkaline pH range is hindered by the carbonate ions.

At eich, however, the treatment with O / on does not lead to the complete breakdown of the organic compounds, but rather to the fact that compounds such as oxalic acid remain in accordance with the statements of the prior art. In both cases, this means a complete breakdown of the organic compounds and thus the TOC to inorganic degradation products such as carbon dioxide and water by treatment with ozone according to the prior art not possible

The present invention is therefore based on the object of providing a process for reducing the content of organic compounds in water which contains dissolved carbonic acid or carbonates

In the event that the water contains dissolved common salt, the present invention is also based on the object of providing a process for reducing the content of organic compounds in the water which contains dissolved carbonic acid or carbonates to such a small extent, that in

Water dissolved table salt can be used to produce Chloi by electrolytic processes

The task according to the invention is solved by a process / treatment of water which has a TOC of more than 2 ppm and contains at least 0.01% by weight of dissolved coal sauce or caibonates, with ozone, characterized in that the treatment is carried out at a temperature of 10 to 130 ° C and at an absolute pressure of 0.5 to 3 bar and that the water which is fed to the process has a pH of 2 to 1 1 and that the treatment over a period of 1 minute to 10 hours.

It has also been found that the water treated according to the invention, if it contains dissolved common salt, can be used to produce chlorine and sodium hydroxide solution by electrolysis of the common salt. In particular, the chlorine can be produced by the known membrane process. The process is not impaired by any impurities that may still be present in very low concentrations; in particular, the service life of the membranes is the same compared to the use of saline solutions, which are obtained by dissolving saline in completely pure water.

The process according to the invention for the treatment of water with ozone is particularly economical, not technically complex and environmentally friendly. No high excess pressure is required. No catalyst is required. No UV radiation is required. There are no other chemicals, such as B. hydrogen peroxide, required. Of course, these measures can also be carried out.

The process according to the invention allows the TOC in water to be reduced to below 1 ppm.

The water treated with ozone according to the invention is also so pure that it can be discharged directly into surface water without the need for further purification. This provides an economical and ecologically favorable way of processing and disposing of water that has a TOC of more than 2 ppm and also contains dissolved carbonic acid or carbonates. According to the invention, the TOC of the water before the treatment with ozone is more than 2 ppm, preferably more than 5 ppm, particularly preferably more than 10 ppm.

According to the invention, the TOC is determined in accordance with DIN 38 409-H 3 using the TOC 500 device from Shimadzu by measuring the content of inorganic carbon (TIC) and the content of inorganic or organic carbon (TC) of the water sample. A constant flow of high-purity, carbon dioxide-free air serves as the carrier gas. For TC measurement, a defined amount of the sample to be analyzed is injected into the TC combustion tube and burned there at 680 ° C on a TC catalyst. After cooling and drying, the resulting carbon dioxide is detected in an infrared analyzer. For the TIC measurement, the sample is acidified with phosphoric acid and the resulting carbon dioxide is expelled from the sample and detected as above. The TOC is then calculated from the measured TIC and TC values as follows: TOC = TC-TIC.

According to the invention, the content of carbonic acid or carbonates in the water is at least 0.1% by weight calculated as carbonate (CO ₃ ^" ). It is preferably at least 0.3% by weight, particularly preferably at least 1.0% by weight.

The treatment according to the invention with ozone takes place at a temperature of 10 to 130 ° C, preferably at 20 to 100 ° C, particularly preferably at 60-90 ° C.

The treatment according to the invention with ozone takes place at an absolute pressure of 0.5 to 3 bar, preferably from 1 to 2 bar, particularly preferably at 1.2 to 1.8 bar.

The water which is fed to the process according to the invention for treatment with ozone has a pH of 2 to 11, preferably it has a pH of 3 to 11, particularly preferably it has a pH of 5 to 9 , very particularly preferably it has a pH of 5.5 to 7. The pH is measured at 20 ° C. A particularly preferred embodiment of the invention is given by the fact that the pH of the water which is fed to the process for treatment with ozone is less than 7 and has a value such that after the treatment of the water with ozone it has a value above 7.5 has. This change in the pH value from the acidic to the basic range in the course of the treatment with ozone leads to a particularly effective breakdown of the TOC in the water. In order to achieve this change in the pH value from the acidic to the basic range, depending on the carbonate content of the water and the possibly present content of other substances which lead to a pH change in the course of the treatment of the water with ozone, the pH of the water added to the process for treatment with ozone is adjusted.

The treatment according to the invention with ozone takes place over a period of 1 minute to 10 hours, preferably from 6 minutes to 2 hours, particularly preferably from 10 minutes to 60 minutes.

In the event that the water which is subjected to the treatment with ozone according to the invention contains dissolved common salt, a preferred embodiment of the present invention is a method in which, after the ozone treatment of the water, the water is subsequently fed to the electrolysis for the production of chlorine. The electrolysis is preferably carried out by the membrane process. The water which is subjected to the treatment with ozone according to the invention contains, for example, 2 to 20% by weight of common salt. It preferably contains 4 to 12% by weight of common salt.

The production of chlorine by electrolysis of table salt is described, for example, in Ullmann ^'s Encyclopedia of Industrial Chemistry, Volume A, 5th May 1986, pages 401 to 477. In particular, the particularly advantageous membrane process is also described on pages 437 to 450 . A prerequisite for the utilization of common salt in the wastewater of polycarbonate production by electrolysis is the degradation of the organics contained in the wastewater to values below approx. This applies in particular if the particularly advantageous membrane process is to be used for chlor-alkali electrolysis.

The water which is subjected to the treatment with ozone according to the invention is preferably the wastewater from polycarbonate production by the phase interface process, particularly preferably it is wastewater from the production of bisphenol A polycarbonate by the phase interface process.

The temperature of the water which is supplied to the treatment with ozone can, for example, be set to the desired value with the aid of a heat exchanger.

The pH of the water added to the treatment with ozone can be adjusted, for example, by adding an acid such as e.g. Hydrochloric acid or an alkali such as B. sodium hydroxide solution to the desired value.

The mixing of the water with the ozone generated in the ozone generator should be carried out as intensively as possible for optimal reaction control. In principle, any form of gas distribution is possible, e.g. the use of ultrasound, glass frits or conventional injectors.

The oxidation of the wastewater with ozone is preferably carried out in a continuous process, with a plurality of reaction columns preferably being connected in series. For as quantitative a decomposition of the TOC as possible, a partial stream of the freshly produced ozone is preferably passed directly to the columns following the first column.

A preferred embodiment of the invention is given in that at least two, in particular three, reaction columns for treatment with ozone are introduced. and that the ozone distribution varies between a distribution of 1: 1 or 1: 1: 1 (volume flow of the 1st column: volume flow of the 2nd column) per column up to 5: 1 or 5: 1: 1. The ozone distribution in the reaction columns is preferably 80% in the first column (s) and 20% in the last column.

Possibly occurring peak loads of the TOC in the water can be adsorbed, for example, by an adsorber column, which is connected upstream of the system for treatment with ozone, and can be supplied to the treatment with ozone in a controlled manner under normal operating conditions. The adsorber column is preferably only used for

Peak loads also operated.

The adsorber column is preferably constructed as follows. The adsorber column is cooled in the jacket by water. This sets an operating temperature of 15 ° C. The adsorber column is filled with adsorbers which adsorb phenol and bisphenol well and, depending on the pH, also desorb again, for example and preferably a microporous, non-functionalized, hydrophilic, hyper-crosslinked copolymer based on styrene and divinylbenzene or activated carbon as adsorber.

The process according to the invention can be used, for example, to treat the waste water from the production of polycarbonate using the phase interface process. The cleaned wastewater can then be used to recover the common salt contained in the water for the production of chlorine by electrolysis. It is advantageous to determine the concentration of salt in the water, for example

4 to 12 wt .-% can be increased by adding solid table salt to a concentration of 20 to 30 wt .-%, preferably 25 wt .-%, before the water is fed to the electrolysis. The chlorine produced in the electrolysis and the sodium hydroxide solution can be fed back to the process for the production of polycarbonate by the phase-surface process after the chlorine has been added Carbon monoxide was converted to phosgene and the sodium hydroxide solution was used, for example, to produce bisphenolate solutions.

The organic compounds that make up the TOC pollution of the water can be any organic compounds. These can be both aliphatic and aromatic compounds. The compounds can contain any heteroatoms. In the case of treatment of waste water from polycarbonate production, the organic compounds consist essentially of phenols (e.g. unsubstituted phenol or alkylphenols or arylphenols or bisphenols such as e.g. bisphenol A) and amines (e.g. triethylamine, ethylpiperidine).

The ozone used in the process according to the invention is produced by known processes, for example from air or from oxygen. This creates mixtures of ozone in air or in oxygen, which contain, for example, 40 to 150 g of ozone per cubic meter of gas and which can be used as such. Higher

Concentrations of ozone can be generated by special enrichment methods (adsorption or desorption processes).

Unused ozone, e.g. B. is contained in the exhaust gas of the system for treating the water with ozone, can be thermally or catalytically decomposed in a residual ozone destroyer.

Further preferred embodiments of the present invention result from the fact that a treatment with hydrogen peroxide is additionally carried out before, during or after the treatment with ozone. Treatment is preferably carried out with

Hydrogen peroxide simultaneously with the treatment with ozone.

Further preferred embodiments of the present invention result from the fact that before, during or after the treatment with ozone there is additionally a treatment by UV radiation. Treatment with UV

Radiation simultaneously with treatment with ozone. Further preferred embodiments of the present invention result from the fact that, before, during or after the treatment with ozone, treatment is additionally carried out with hydrogen peroxide and with UV radiation. The treatment with hydrogen peroxide and with UV radiation is preferably carried out simultaneously with the

Treatment with ozone.

The invention is explained below with reference to a drawing showing a preferred embodiment (FIG. 1).

The water is brought to the desired temperature by the heat exchanger 1. The adsorber column 2 is only flowed through when the TOC content is exceptionally high. Appropriate valves are available for this. If the TOC content is low, the adsorber can also be flowed through to desorb the TOC again. The appropriately tempered water becomes

Adjustment of the pH in the stirred tank 3 mixed with hydrochloric acid 4. The treatment with ozone then takes place in columns 5 and 6. Because of the high corrosion potential of the ozone-oxygen mixture in water, both columns preferably consist of titanium. The water is conveyed by the pump 7. The columns can be heated and are connected to one another by an overflow. The heat exchangers

8 and 9 serve to condense any water that has been entrained (stripped) with the gas flow. The ozone is generated from oxygen in the ozone generator 10 and mixed with the waste water via a nozzle 11 and 12 at the entrance of the columns. Unused ozone is thermally destroyed in the residual ozone destroyer 13, preferably at 250 to 300 ° C.

For the analytical examination of the tests, three sampling points 14 (zero sample), 15 (after the first column) and 16 (after the second column) were installed for the removal of the treated waste water. The ozone concentration is after the ozone generator and after the heat exchangers 8 and 9 by the measuring points 17,

18, 19 and 20 determined. The invention is illustrated below by examples.

In the pilot plant shown in FIG. 1, the wastewater from the production of bisphenol A homopolycarbonate was treated using the phase interface method with different amounts of ozone at different temperatures and different pH values. The exact test conditions and results can be found in Tables 1 (examples according to the invention) and 2 (comparative examples).

The water which was fed to the process contained 4 to 12% by weight of common salt and 0.3 to 1.5% by weight of carbonate. The TOC values of the water are given in the tables. The TOC resulted essentially from phenol and bisphenol A.

As the experiments show, it is particularly advantageous to set an input pH of less than 7 and a to reduce the TOC to values around 1 ppm

Set temperature between 60 and 90 ° C. In the course of the reaction, a pH value of over 7 is established in column 1 and a pH value of 8 is obtained after column 2. This change in pH value is based on the fact that the CO2 contained in the waste water is only partially neutralized can escape and only escapes in the columns, so that there is an associated increase in pH. This is accompanied by a change in the reaction mechanism from oxidation to

Attack of ozone on oxidation by attack with hydroxyl radicals. The attack of ozone leads to the breakdown of the phenols and the formation of breakdown products, which are then broken down by the hydroxyl radicals.

Table 1 (examples according to the invention)

Table 1 (continued)

Table 2:

(Comparative examples; pH value of the water before ozone treatment: 12, temperature of the water before ozone treatment: 60 ° C)

Claims

claims Process for the treatment of water, which has a TOC of more than 2 ppm and contains at least 0.1% by weight of dissolved carbonic acid or carbonates, with ozone, characterized in that the treatment at a temperature of 10 to 130 ° C and at an absolute pressure of 0.5 to 3 bar and that the pH of the water which is fed to the process is 2 to 1 1 and that the treatment is carried out over a period of 1 minute to 10 hours. A method according to claim 1, wherein the water contains 2 to 20 wt .-% sodium chloride. 3. A process for the production of chlorine by electrolysis of sodium chloride, characterized in that the sodium chloride in the electrolysis process Is supplied in the form of an aqueous solution which is obtained by treating water which has a TOC of more than 2 ppm and a saline content of 2 to 20% by weight and contains at least 0.1% by weight of dissolved carbonic acid or carbonates, with ozone, the treatment with ozone at a temperature of 10 to 130 ° C and at an absolute Pressure of 0.5 to 3 bar is carried out and the pH of the water which is fed to the process for treatment with ozone is 2 to 11 and the treatment with ozone takes place over a period of 1 minute to 10 hours . A method according to claim 3, wherein the electrolysis is carried out by the membrane method. A process according to any one of claims 1 to 4, wherein the water which is subjected to the treatment with ozone according to the invention is the waste water from the production of polycarbonate by the phase interface process. 6. The method according to claim 5, wherein the water which is subjected to the treatment with ozone according to the invention is the waste water from the production of bisphenol-A polycarbonate by the phase interface process. 7. The method according to any one of claims 1 to 6, wherein the pH of the water which is supplied to the process for treatment with ozone is less than 7 and has a value such that it has a value after the treatment of the water with ozone over 7.5.